Sorry if some terminology I use might be inadequate, I don't have any formal education in this area and I'm not a native English speaker.

A species evolves through natural selection to become more well adapted to the environment that surrounds it, however, the direction in which a species evolves doesn't seem to be only a function of how well it does finding food and escaping predators, in many cases it also involves some competition between males which are then evaluated and chosen by females due to some subjective criteria they use.

So I think it is fair to say that it is the female's criteria for that evaluation that determines the direction of the evolution of that species, i.e., if female's main criteria is the size of the horns, the species' horn size will tend to increase.

So where did that criteria came from? The most reasonable conclusion, to me, is that it has evolved as an analog to what ends up improving survival odds odds of the species. In some way, bigger horns must be (or have been) useful in escaping predators so females that happened to choose males with bigger horns got their offspring genes better chances of survival, perpetuating that criteria in future females. So that criteria can be seen as a shortcut, a way to accelerate evolution in a certain direction if that direction has proven to be more useful than others.

However, isn't that criteria in some species much removed from their actual survival odds? I mean, lets look at a peacock, the main selection criteria seems to be the size, colors and/or patterns of the male's tail and it is hard to see how evolving in that direction to the amazing lengths that we see today, would have helped them survive any better than if they had used other more usual criteria.

Any thoughts about this? Am I right about the way these evaluation criteria evolve? Is there any literature about this that you can point me to? Thanks!

What do you mean by health? I mean, what is the female really testing? Is it the absence of disease or is it health in the sense that the animal would need a constant influx of nutrients in order to develop that tail? Because if it's the later, then it must still point to a functional advantage in gathering food or staying alive longer, which was essentially what I was defending. If it's the former, and without any more information, I'm a little skeptical.

In that view, the peacock's tail or the deer horns are not adaptations to the environment, they're just byproducts of evolution that are used for testing something unrelated with any functional advantage of having tails with that size/shape/color/pattern. More than being unrelated with an advantage, I would say they would act as a disadvantage because of the added nutrients required for its production, added energy required to carry that weight around and, in the peacocks case in particular, because it would make them slower.

Maybe that's not a problem for peacocks, I don't know how much they suffer from predation, but as a generalization, it seems counter-intuitive that creatures tend to develop these costly device to test something that would be much more easily tested some other way. On the other hand, it would explain the peacock's particular case much more easily.

Oh certainly there are different ways for the female to test the fitness of the male, some birds require some sort of "gift" of food or a well made nest before mating so in those cases it might seem more pragmatic.

I don't know why peacocks developed the tail as opposed to other methods of showing their healthiness but certainly you're right in that the tail is a burden and it seems the male is saying "look at me, in spite of this disadvantage, I am still alive"...possibly hinting that he is healthy and capable in other ways as well.

Living one day at a time; Enjoying one moment at a time; Accepting hardships as the pathway to peace; ~Niebuhr

Darby wrote:Also, things like horn size are not really female-choice markers, but affect male access to females: they go through combat, for which horn size is just one factor.

Good point. If the female's strategy is to choose the male that other males see as dominant then whatever drives evolution has mainly to do with whatever gives a male an advantage in combat against other males from the same species. It seems to me that such strategy could lead to "wrong" results though, in the sense that those advantages might not necessarily translate to a better adaptation to the environment they live in and their predators. This could explain some odd things in nature that doesn't seem to follow from abiotic factors and adaptation pressures from predators/prey. The peacock's tail still intrigue me though.

However, that by itself wouldn't explain why the females adopted that criteria in the first place. I can see two options, maybe they don't really have a choice because other non-dominant males show themselves as unavailable in the presence of the dominant male. This would mean that they're not really choosing since they're "choosing" the only available male so the strategy was imposed on them, so to speak. The strategy would still need to have proven useful for the species adaptation to the environment given the fact that the mechanism has evolved and survived to this day.

Another option is that females adopted this strategy because the results of physical combat between males actually provides an accurate translation to survival odds in that particular environment.

On either case, directly or more indirectly, bigger horns should still provide the species with some functional advantage in their environment otherwise we could say that the mate selection mechanism is not optimal in that case because it's creating internal pressures that are leading to significant changes that aren't benefiting the species as a whole.

Scientists observed of the MHC results of some human, and then they match it with other shuffle made controlled. scientist observed the ratio of MHC matching between them who were real, and match it with in the differently generated 'virtual. It is a huge genetic region based on chromosome 6, and may be find the most vertebrates. Thus we believe to know some cultural factors that play an important role in mate selection, and hopefully do not works to the theory on if a person bears a specific genetic variation.